Not Applicable
The present invention relates to a sealing arrangement for sealing a space, which extends between high and low pressure areas and which is defined between a first apparatus part and a cylindrical surface of a second apparatus part, the first and second apparatus parts being mutually movable in a reciprocating manner along the axis of said cylindrical surface.
As an example, the apparatus part may be part of a housing or a cylinder, and the second apparatus part may be a piston rod connected to a double acting piston. A sealing arrangement of this type is disclosed for example in WO 92/15807. This known sealing arrangement comprises an annular sealing member of resilient material and a compression ring, such as an O-ring, surrounding the annular sealing member. The radially outer peripheral surface of the annular sealing member extends between axially opposite first and second end surfaces facing said high and low pressure areas, respectively. The annular sealing member also has a radially inner peripheral surface for sealing engagement with the cylindrical surface of the second apparatus part at a contact area thereof. The purpose of the compression ring is to press the contact area of the inner peripheral surface of the sealing member into tight sealing engagement with the cylindrical surface of the second apparatus part. This means that ideally the annular contact area between the compression ring and the outer peripheral surface of the annular sealing member should be positioned radially opposite to the contact area between the sealing member and the cylindrical surface of the second apparatus part.
In actual practice, however, the pressure difference between the high and low pressure areas varies substantially, and an increasing pressure difference tends to force the compression ring and, consequently, also the contact area between the compression ring and the annular sealing member, in a direction toward the low pressure area. In order to substantially maintain the sealing pressure between the contact area of the inner peripheral surface part of the sealing member and the cylindrical surface of the second apparatus part when the compression ring is forced toward the low pressure area, the outer peripheral surface of the sealing member is chamfered at its low pressure end. Thus, the annular sealing member of the known sealing arrangement has an outer peripheral surface defining an obtuse angle in an axial sectional view.
It has been found that the compression ring, which may, for example, be an O-ring made from an elastomeric material, has a relatively short useful lifetime, because eventually the compression ring becomes permanently deformed.
The present invention provides a sealing arrangement of the type discussed above with an increased efficiency and a prolonged useful economic lifetime.
Thus, the present invention provides a sealing arrangement for sealing a space, which extends between high and low pressure areas and which is defined between a first apparatus part and a cylindrical surface of a second apparatus part, the first and second apparatus parts being mutually moveable in a reciprocating manner along the axis of said cylindrical surface, said sealing arrangement comprising an annular sealing member of resilient material having a radially outer peripheral surface extending between axially opposite first and second end surfaces facing said high and low pressure areas, respectively, and a radially inner peripheral surface for providing a sealing engagement with the cylindrical surface of the second apparatus part at a contact area, and for defining with the cylindrical surface a first space widening or diverging from said contact area towards the low pressure area; and a compression ring surrounding the annular sealing member, the compression ring being in contact with the outer peripheral surface of the annular sealing member so as to press the inner peripheral surface thereof into close contact with the cylindrical surface of the second apparatus part at said contact area; the axial sectional view of at least part of the outer peripheral surface of the annular sealing member coming into contact with the compression ring defining such convex contour that in an unstressed condition of the sealing member, the radial distance between such part of the outer peripheral surface and the radially innermost part of the inner peripheral surface is decreasing in an axial direction toward the second end surface and the low pressure area, the radius or radii of curvature of the convex contour being at least 0.4 times the total axial length or width of the annular sealing member.
It has been found that in the known sealing arrangements the efficiency of the compression ring is eventually reduced because during operation the compression ring is pressed into contact with a rather sharp annular edge defined by the outer peripheral surface of the sealing member and corresponding to the vertex of the aforesaid obtuse angle. It has been found that the useful lifetime of the sealing arrangement according to the invention is substantially prolonged compared with the lifetime of the known sealing arrangements when the convex contour of the outer peripheral surface of the annular sealing member is rounded as described above.
The radius of curvature of such rounded surfaces preferably does not exceed twice the total axial length or width of the annular sealing member, and in the presently preferred embodiment the radius or radii of curvature is/are at least 0.6 and preferably about 0.85 times the total axial length of the annular sealing member.
The convex contour of the outer peripheral surface of the sealing member may extend along the total axial length or width of the sealing member. However, when the radial distance between the outer peripheral surface of the sealing member and the cylindrical surface of the second apparatus part is gradually decreasing toward the second end surface of the sealing member or toward the low pressure area, the compression ring may tend to be forced or extruded into the space defined between the second end surface of the sealing member and an adjacent opposite surface of the first apparatus part. In order to counteract such tendency, the convex axial sectional contour of the outer peripheral surface part may continuously merge into a concave sectional contour adjacent to the second end surface of the sealing member. In such case the convex contour may merge into the concave contour at an inflexion spaced from said second end surface by a distance of 0.05-0.25 times the total axial length or width of the sealing member. The end part of the sectional contour adjacent to the second end surface of the sealing member and the longitudinal axis of the sealing arrangement preferably defines therebetween an angle from xe2x88x9210xc2x0 to +45xc2x0. Thus, the end part of the sectional contour and the longitudinal axis of the sealing arrangement may be converging, but are preferably diverging toward the low pressure area.
The radially inner peripheral surface of the sealing member may include a first section, which extends between the first end surface of the sealing member and the contact area, and which has a minimum diameter substantially exceeding the maximum diameter of a second section of the inner peripheral surface defining said gradually widening or diverging space. Thus, the contacting area is defined as an intermediate part between the first and second sections. Thereby it is secured that the radially inwardly directed pressure applied by the compression ring is concentrated at the predetermined contact area.
The sealing member and the compression ring of the sealing arrangement according to the invention may be retained in their mutual positions in any suitable manner. In the preferred embodiment, however, the annular sealing member and the compression ring are arranged within an annular channel or groove which is formed in the first apparatus part and defines an annular opening opposite the cylindrical surface of the second apparatus part, said channel having a bottom wall for sealing engagement with the compression ring, and opposite first and second side walls positioned opposite to the first and second end surfaces, respectively, of the sealing member.
According to a further embodiment of the sealing arrangement, the outer peripheral surface of the sealing member may define a convex axial contour having a first section adjacent to the first end surface of the sealing member and a second section adjacent to the second end surface of the sealing member, the first and second end sections being interconnected by an intermediate section, and the radial height or width of the cross-section of the annular sealing member may then be a maximum at the intermediate section. By suitably selecting the mutual actual positions of the intermediate section of the outer peripheral surface and the contact section of the inner peripheral surface of the sealing member, the radial compressive force applied the compressive ring may be optimized so as to obtain an optimum sealing effect. In a preferred embodiment, the first section at least along an axial length of from 0.3 to 0.7 times the total axial length of the sealing member measured from said second end surface defines an angle of between 0xc2x0 and 20xc2x0 with the longitudinal axis of the sealing member.
According to a second aspect, the present invention provides an annular sealing member of resilient material for sealing a space, which extends between high and low pressure areas and which is defined between a first apparatus part and a cylindrical surface of a second apparatus part, said sealing member having a radially outer peripheral surface extending between axially opposite first and second end surfaces for facing said high and low pressure areas, respectively, and a radially inner peripheral surface for sealing engagement with the cylindrical surface of the second apparatus part at a contact area and for defining, with the cylindrical surface, a first space widening for said contact area towards the low pressure area, the axial sectional view of at least part of the outer peripheral surface of the annular sealing member, which is adapted to come into contact with the compression ring, defining such convex contour that in an unstressed condition of the sealing member the radial distance between such part of the outer peripheral surface and the radially innermost part of the inner peripheral surface is decreasing in an axial direction towards the second end surface, the radius or radii of curvature of the convex shape being at least 0.4 times the total axial length or width of the annular sealing member. Because a convex shape does not have sharp edges, the useful lifetime of the sealing member and of the compression ring co-operating therewith is extended.
International Publication WO 92/15807 discloses a sealing arrangement comprising an annular sealing member. The sealing member has a radially inner peripheral surface which is divided into three axial sections, namely a first section adjacent to the high pressure area, an intermediate section forming a predetermined contact area, and a second section adjacent to the low pressure area. The first section is defined by a stepped part having an inner diameter substantially exceeding the outer diameter of a cylindrical surface of a second apparatus part or piston rod. The intermediate predetermined contact area is adapted to be in sealing engagement with the outer cylindrical surface of the piston rod, and the second section is a conical surface defining a widening or diverging space together with the outer cylindrical surface of the piston rod. In the known sealing arrangement the borderline between the contact area and the second section of the inner peripheral surface part of the sealing member is defined by an annular edge. However, when the pressure difference exceeds a certain value, for example on the order of 300 bar, and/or when the temperature becomes excessively high, the sealing member may tend to tilt about the edge or to deform such that part of the second section of the inner peripheral surface part of the annular sealing member comes into contact with the outer cylindrical surface of the second apparatus part. This may result not only in a less efficient sealing effect, but also in so-called extrusion damages of the sealing member.
The present invention solves these problems. Thus, the present invention provides a sealing arrangement for sealing a space, which extends between high and low pressure areas and which is defined between a first apparatus part and a cylindrical surface of a second apparatus part, the first and second apparatus parts being mutually moveable in a reciprocating manner along the axis of the cylindrical surface, the sealing arrangement comprising an annular sealing member of resilient material having a radially outer peripheral surface extending between axially opposite first and second end surfaces facing the high and low pressure areas, respectively, and a radially inner peripheral surface for sealing engagement with the cylindrical surface of the second apparatus part at a contact area, and for defining with the cylindrical surface a first space widening from the contact area toward the low pressure area; and annular compression means for pressing the inner peripheral surface thereof into close contact with the cylindrical surface of the second apparatus part at the contact area; the widening space being defined by an inner peripheral surface section extending between the contact area and the second end surface, the axial sectional view of the surface section defining a convex, rounded contour with a radius or radii of curvature selected so as to improve the sealing characteristics of the sealing member.
The annular compression means may, for example, comprise a compression ring engaging with the radially outer peripheral surface of the sealing member. The outer peripheral surface of the annular sealing member may have a linear or convex cross-sectional shape. Alternatively, the outer peripheral surface of the sealing member may comprise a concave surface part engaging with a complementary convex surface part of the annular compression means.
The annular compression means may be a compression ring made from an elastomeric material and having a solid cross-section. The compression ring may then be divided into a pair of axially juxtaposed annular members. Alternatively, the compression means may be made from metal. such as a helically wound wire. Furthermore, the annular sealing member need not be a single uniform part, but may be divided into two or more parts having mutually engaging complementary surface parts. Such sealing member parts maybe separate or bound together and may be made from materials having different characteristics.
According to another embodiment, the compression means may be positioned within a pocket, which is defined within the annular sealing member and which opens into the first end surface of the sealing member. As an example, the compression means may then be an annular metal spring member having a U-shaped cross-section tending to open the pocket and thereby expand the cross-section of the sealing member radially.
In the preferred embodiment, the radius or radii of curvature is/are within the range of from 0.15 to 1.5, preferably 0.2 to 0.6, and more preferably approximately 0.3, times the total axial length or width of the sealing member. By selecting an axial contour of the inner peripheral surface of the annular sealing member with such predetermined convex, rounded contour, improved sealing characteristics may be obtained, especially in case of an excessive pressure difference between the high and low pressure areas and/or at high temperatures.
As mentioned above, the inner peripheral surface of the annular sealing member may be divided into three parts each extending along a fraction of the total axial length of the annular sealing member. As an example, the inner surface section defining the widening space and being adjacent to the second end surface of the sealing member preferably does not have an axial length exceeding 0.3 times the total axial length of the sealing member. The contact of area of the inner peripheral surface part is preferably located within the axial length range of from 0.2 to 0.6 times the total axial length of the sealing member measured from the second end surface. Furthermore, this contact area preferably defines a convex, rounded contour with a radius or radii of curvature within the range of from 2 to 5 times the total axial length of the sealing member. The outer peripheral surface of the annular sealing member may be shaped as previously explained.
The present invention further provides an annular sealing member of resilient material for sealing a space, which extends between high and low pressure areas and which is defined between a first apparatus part and a cylindrical surface of a second apparatus part, the first and second apparatus parts being mutually moveable in a reciprocating manner along the axis of the cylindrical surface, the sealing member having a radially outer peripheral surface extending between axially opposite first and second end surfaces for facing the high and low pressure areas, respectively, and a radially inner peripheral surface adapted to be pressed into sealing engagement with the cylindrical surface of the second apparatus part at a contact area and for defining with the cylindrical surface a first space widening from the contact area toward the low pressure area, the widening space being defined by an inner peripheral surface section extending between the contact area and the second end surface, the axial sectional view of the surface section defining a convex, rounded contour with a radius or radii of curvature selected so as to improve the sealing characteristics of the sealing member. Such sealing member may, for example, be used in a sealing arrangement as described above.